I now proceed to show in what sense we are really to understand the words, that we must be converted and become like little children. The Evangelist tell us, 'that the disciples at this time came unto Jesus, saying, Who is the greatest in the kingdom of heaven?' These disciples had imbibed the common prevailing notion, that the Lord Jesus Christ was to be a temporal prince. They dreamed of nothing but being ministers of state, of sitting on Christ's right hand in his kingdom and lording it over God's people. They thought themselves qualified for state offices, as generally ignorant people are apt to conceive of themselves. Well, say they, 'Who is the greatest in the kingdom of heaven?' Which of us shall have the chief management of public affairs?
So that what our Lord is speaking of is not the innocency of little children, if you consider the relation they stand in to God and as they are in themselves when brought into the world. But what our Lord means is that as to ambition and lust after the world we must in this sense become as little children. . . . Now in this sense we must be converted and become as little children, that is, we must be as loose to the world, comparatively speaking, as a little child.
When our Lord says, we must be converted and become as little children, I suppose he means also, that we must be sensible of our weakness, comparatively speaking, as a little child. . . . Are little children sensible of their weakness? Must they be led by the hand? Must we take hold of them or they will fall? So, if we are converted, if the grace of God be really in our hearts, my dear friends, however we may have thought of ourselves once, whatever were our former high exalted imaginations, yet we shall now be sensible of our weakness.
And as little children look upon themselves to be ignorant creatures, so those that are converted do look upon themselves as ignorant too. Hence it is, that John speaking to Christians calls them little children: 'I have written unto you, little children.' . . . Hence that great man . . . the Apostle Paul, when he speaks of himself, says, 'Unto me, who am less than the least of all saints, is this grace given, that I should preach among the Gentiles the unsearchable riches of Christ.' . . .
And as a little child is looked upon as an harmless creature and generally speaks true so, if we are converted and become as little children, we shall be guileless as well as harmless. What said the dear Redeemer when he saw Nathanael? As though it was a rare sight he gazed upon and would have others gaze upon it: 'Behold an Israelite indeed.' Why so? 'In whom is no guile.' Do not mistake me, I am not saying that Christians ought not to be prudent. They ought exceedingly to pray to God for prudence, otherwise they may follow the delusions of the devil and by their imprudence give wrong touches to the ark of God. . . . We should pray for the wisdom of the serpent, though we shall generally learn this wisdom by our blunders and imprudence. And we must make some advance in Christianity before we know our imprudence.
—George Whitefield, "Marks of a True Conversion" in Lee Gatiss (Ed.), The Sermons of George Whitefield (Crossway, 2012), 1:390–393.